Investigation of Copper(II) Interference on the Anodic Stripping Voltammetry of Lead(II) and Cadmium(II) at Bismuth Film Electrode

The bismuth‐coated electrode is known to be prone to errors caused by copper(II). This study investigates copper(II) interference at bismuth film electrode for the detection of lead(II) and cadmium(II). It was conducted using glassy carbon electrode, while the bismuth film was plated in situ simultaneously with the target metal ions at ? 1200 mV. Copper(II) presented in solution significantly reduced the sensitivity of the electrode, for example there was an approximately 70 % and 90 % decrease in peak signals for lead(II) and cadmium(II), respectively, at a 10‐fold molar excess of copper(II). The decrease in sensitivity was ascribed to the competition between copper and bismuth or the metal ions for surface active sites. Scanning electron microscopy (SEM) and energy dispersive X‐ray (EDX) analysis suggested a large decrease in the amount of bismuth nanoparticles formed on the electrode surface in the presence of copper(II) occurred, validating the competition between copper and bismuth ions for surface active sites. Recovery of the stripping signal of lead(II) and cadmium(II) was obtained by adding ferrocyanide ion to the solution. Finally, the proposed method was successfully applied to determine lead(II) and cadmium(II) in water samples and the method was validated by ICP‐MS technique.     

Stripping chronopotentiometric measurements of lead(II) and cadmium(II) in soils extracts and wastewaters using a bismuth film screen-printed electrode assembly

The key to remediative processes is the ability to measure toxic contaminants on-site using simple and cheap sensing devices, which are field-portable and can facilitate more rapid decision-making. A three-electrode configuration system has been fabricated using low-cost screen-printing (thick-film) technology and this coupled with a portable electrochemical instrument has provided a a relatively inexpensive on-site detector for trace levels of toxic metals. The carbon surface of the screen-printed working electrode is used as a substrate for in situ deposition of a metallic film of bismuth, which allows the electrochemical preconcentration of metal ions. Lead and cadmium were simultaneously detected using stripping chronopotentiometry at the bismuth film electrode. Detection limits of 8 and 10 ppb were obtained for cadmium(II) and lead(II), respectively, for a deposition time of 120 s. The developed method was applied to the determination of lead and cadmium in soils extracts and wastewaters obtained from polluted sites. For comparison purposes, a mercury film electrode and ICP-MS were also used for validation.     

Thermodynamics of interactions between lead(II) and cadmium(II) ions and azulene-based complexing polymer films

In order to understand the essential processes/interactions between the metal ions and modified electrodes which are based on complexing polymeric films, access to thermodynamic characteristics is compulsory. The paper enlarges the information concerning the sorption of metal ions within complexing polymer films, particularly based on azulene, which can be involved in metal detection sensors. Interactions between lead(II) or cadmium(II) ions and complexing polymer films have been studied using chemical preconcentration–anodic stripping method. The films have been obtained by controlled potential electrolysis in millimolar solutions of 4-azulen-1-yl-2,6-bis(2-thienyl)pyridine (L) in acetonitrile. PolyL films affinities towards these metal ions have been quantified at different temperatures by means of sorption isotherms. Parameters for sorption of lead(II) and cadmium(II) ions within polyL films have been calculated for Freundlich, Langmuir and Redlich–Peterson isotherms. The best fit was obtained when using Langmuir isotherm. The results evidence that lead ions are better sorbed than cadmium within polyL film. Thermodynamic parameters for the chemical sorption of lead(II) and cadmium(II) ions within polyL films have been calculated.     

Electroanalytical determination of cadmium(II) and lead(II) using an in-situ bismuth film modified edge plane pyrolytic graphite electrode.

A highly sensitive and simple electroanalytical methodology is presented using an in-situ bismuth film modified edge plane pyrolytic graphite electrode (BiF-EPPGE) which is exemplified with the simultaneous determination of cadmium(II) and lead(II). Square-wave anodic stripping voltammetry is utilised with the effects of several experimental variables studied. Simultaneous additions of cadmium(II) and lead(II) were investigated where two linear ranges between 0.1-100 and 0.1-300 microg/L and also detection limits of 0.062 and 0.084 microg/L were obtained, respectively. The method was then successfully applied to the simultaneous determination of cadmium(II) and lead(II) in spiked river water, where recoveries of 100.5 and 98% were obtained, respectively. This electroanalytical protocol using edge plane pyrolytic graphite electrodes is one of the simplest methodologies to date using non-mercury based electrodes and is simpler and cheaper than alternatives such as carbon nanotube electrode arrays, suggesting the use of edge plane pyrolytic graphite electrode for routine sensing.     

Determination of cadmium(II) at a gold electrode in the presence of selenium(IV) by anodic-stripping voltammetry with enhancement by iodide ion

Anodic-stripping voltammetry (ASV) has been used in the derivative mode for the determination of cadmium, with a gold electrode in sulphuric add medium containing seleniurn(IV). The peak height for cadmium is enhanced by the presence of iodide. The sensitivity for cadmium is very high, with a peak in the stripping voltamperogram at -0.27V (vs. Ag/AgCl). The peak height for cadmium is not affected by over a 100-fold level of lead in the presence of selenium(IV). The dependence of peak height on the cadmium concentration is linear in the range 0.05-10ng ml .     

Chromatographic separation of In(III) from Cd(II) in aqueous solutions using commercial resin (Dowex 50W-X8)

This work assesses the potential of an adsorptive material, Dowex 50w-x8, for the separation of indium ions from cadmium ions in aqueous media. The adsorption behavior of Dowex 50 w-x8 for indium and cadmium ions was investigated. The effect of pH, initial concentration of metal ions, the weight of resins, and contact time on the sorption of each of the metal ions were determined. It was found that the adsorption percentage of the indium ions was more than 99% at pH 4.0. The result shows that In (III) was most strongly extracted, while Cd(II) was slightly extracted at this pH value. The recovery of In(III) and Cd(II) ions is around 98% using hydrochloric acid as the best eluent.      

Simultaneous determination of cadmium(II), lead(II) and copper(II) by using a screen-printed electrode modified with mercury nano-droplets

We are presenting a strategy for the fabrication of disposable screen-printed electrodes modified with mercury nano-droplets and capable of sensing heavy metal ions. They were prepared by coating electrodes with a mixture of multi-walled carbon nanotubes and chitosan, this followed by adsorption of mercury. The resulting sensor was characterized by cyclic voltammetry and impedance spectroscopy. Also the effects caused by adsorption of mercury were investigated. It is shown that square wave anodic stripping voltammetry enables simultaneous determination of cadmium(II), lead(II) and copper(II), for which detection limits of 12, 23 and 20 nM, respectively, are found. Relative standard deviations for ten determinations at 0.6 µM concentrations of these ions are in the range of 3.0 to 5.7%. The applicability was tested by analyzing river water and showed recoveries between 94.1 and 104.6%, thus demonstrating its utility for in-field monitoring of these heavy metal ions.     

General characteristics of the copper-based mercury film electrode

The optimum conditions for the preparation, storage, conditioning and renewal of copper-based mercury film electrodes (CBMFEs) are given. The voltammetric results obtained at these electrodes are compared with the predictions of the theory of cyclic and stripping voltammetry at the mercury film electrode, as well as with the results obtained at the silver-based and the platinum-based mercury film electrodes. The advantage of a CBMFE is prolonged life-time, whereas the disadvantages ar the decreased range of usable positive potentials and the possibility of interfering reactions of the electrodeposited metals with the copper substrate or copper dissolved in the mercury phase. The presence of copper has no essential influence on the behaviour of lead and thallium; it affects the behaviour of zinc markedly and that of cadmium and indium slightly. The conditions allowing the minimization of the harmful action of copper on the behaviour of cadmium and indium have been found.     

Effect of mercury(II) on metal complex labilities determined by direct-current anodic stripping voltammetry on a thin mercury film electrode

The labilities of copper, lead and cadmium complexes with fulvic acid, nitrilotriacetic acid and an iron-humic acid colloid were studied on a preplated thin mercury film electrode and with in-situ plating of mercury on a glassy carbon electrode. In the presence of mercury(II) the apparent labilities based on direct-current anodic stripping voltammetric peak-area measurements increased for each of the cadmium and lead species and for the copper iron-humic acid colloid species. In contrast, for the copper complexes with nitrilotriacetic acid and fulvic acid the lability was not measurably altered by mercury(II); it is inferred that they do not undergo rapid metal exchange with mercury(II).     

Modification of carbon screen-printed electrodes by adsorption of chemically synthesized Bi nanoparticles for the voltammetric stripping detection of Zn(II), Cd(II) and Pb(II)

A simple procedure for the chemical synthesis of bismuth nanoparticles and subsequent adsorption on commercial screen-printed carbon electrodes offer reliable quantitation of trace zinc, cadmium and lead by anodic stripping square-wave voltammetry in nondeareated water samples. The influence of two hydrodynamic configurations (convective cell and flow cell) and the effect of various experimental variables upon the stripping signals at the bismuth-coated sensor are explored. The square-wave peak current signal is linear over the low ng mL⁻¹ range (120 s deposition), with detections limits ranging from 0.9 to 4.9 ng mL⁻¹ and good precision. Applicability to waste water certified reference material and drinking water samples is demonstrated. The attractive behaviour of the new disposable Bi nanoparticles modified carbon strip electrodes, coupled with the negligible toxicity of bismuth, hold great promise for decentralized heavy metal testing in environmental and industrial effluents waters.     

The Use of the Bismuth Film Electrode for the Anodic Stripping Voltammetric Determination of Tin

Bismuth coated glassy carbon electrodes have been applied to the square‐wave anodic stripping voltammetry (SWASV) of trace concentrations of tin. Optimization of Bismuth Film Electrode (BFE) performance was conducted after initial comparison with the more traditional mercury electrode. Simultaneous deposition of tin and bismuth at ?1.3 V for 2 minutes in a supporting electrolyte of 2.5 M sodium bromide utilizing a square‐wave stripping step, allowed analysis of tin at the μg L^?1 level. Parameters, such as deposition potential and time, bismuth concentration, square‐waveform settings including amplitude, step height and frequency were studied and optimized. The dependence of stripping current on deposition time indicates that using longer deposition time should facilitate sub μg L^?1 analysis. Tin was analyzed simultaneously with cadmium and either indium or thallium; Where as lead and copper were not resolved from the stripping peaks of tin and bismuth respectively. Finally, the method was applied to the analysis of tin in fruit juice.     

Ultrasensitive and selective measurements of tin by adsorptive stripping voltammetry of the tin-tropolone complex

Trace levels of tin can be determined by voltammetry after controlled adsorptive preconcentration of the tin-tropolone complex on a hanging mercury drop electrode. The resulting adsorptive stripping procedure offers better sensitivity and selectivity than conventional stripping methods for tin. Optimal conditions include 4 x 10(-6)M tropolone in a stirred acetate buffer (pH 4.0), a preconcentration potential of -0.40 V, and differential-pulse stripping. For an 8-min preconcentration period, the detection limit is 2.3 x 10(-10)M (28 ng/l.). Linear calibration plots of i(p)vs. C are obtained at low concentrations, with linear plots of 1/i(p)vs. 1/C at high concentrations. The relative standard deviation (at the 6-mug/1. level) is 2.6%. The response is not affected by the presence of lead, cadmium, indium and thallium, which commonly interfere severely in analogous anodic stripping measurements. Results are reported for river and orange-juice samples.     

Determination of Cd(II) in Some Foodstuffs by Anodic Stripping Pulse Voltammetry (ASPV) using Glassy Carbon Electrode

Abstract

Cadmium in the presence of 0.04 M NaCl as the electrolyte was determined using stripping voltammetry with superimposed constant amplitude pulses of negative polarity (SVPNP) or positive polarity (SVPPP), and differential pulses stripping voltammetry using rotating disc glass carbon electrode (RDGCE). The SVPNP was found to give the greatest sensitivity. The anodic peak was obtained at potential ?850 to ?795 mV due to the oxidation of cadmium to cadmium(II). Linear calibration curves were obtained in the concentration range between 1.5×10^?9–2×10^?10 M. The relative standard deviation is 4.25% at very low concentration of 2×10^?10 M. This method was successfully applied to the determination of cadmium in some foodstuffs (wheat and its products, vegetables) after acid digestion.     

Development of cysteine-modified screen-printed electrode for the chronopotentiometric stripping analysis of cadmium(II) in wastewater and soil extracts

Screen-printed carbon electrodes were fabricated with amino acid functionality by using in situ co-deposition of mercury and cysteine. The three-electrode configuration (graphite carbon working electrode, carbon counter electrode and silver/silver chloride reference electrode) incorporating a cysteine-modified working electrode exhibited good sensitivity towards cadmium(II). Several experimental variables affecting the sensor stripping response were characterised and optimised. These include cysteine and mercury concentrations, deposition time, deposition potential and stripping current. Surface analysis was also conducted using scanning electron microscopy (SEM) in order to characterize the electrode surface during cadmium analysis. The stripping chronopotentiometric response for cadmium(II) was linear in the concentration range 0.4–800 g L^–1 when a deposition time of 2 min was used. A detection limit of 0.4 g L^–1 was obtained using 0.025 M Tris–HCl buffer containing 0.1 M KCl (pH 7.4) as the supporting electrolyte. The analytical utility of the cysteine-modified sensor was demonstrated by applying it to cadmium analysis in various wastewater and soil samples collected from a contaminated site and extracted using acetic acid. The results obtained using the developed electrodes agreed satisfactorily with the values achieved using atomic absorption spectrometry and inductively coupled plasma mass spectrometry analysis. These results demonstrate the feasibility of using this type of sensor for cadmium analysis.     

Bismuth-dispersed xerogel-based composite films for trace Pb(II) and Cd(II) voltammetric determination

We report for the first time the synthesis of bismuth-modified (3-mercaptopropyl) trimethoxysilane (MPTMS) and its application for the determination of lead and cadmium by anodic stripping voltammetry. Xerogels made from bismuth-modified MPTMS and mixtures of it with tetraethoxysilane, under basic conditions (NH₃·H₂O), were characterized with scanning electron microscopy, energy dispersive spectroscopy, infrared spectroscopy and electrochemical methods. Bismuth-modified xerogels were mixed with 1.5% (v/v) Nafion in ethanol and applied on glassy carbon electrodes. During the electrolytic reductive deposition step, the bismuth compound on the electrode surface was reduced to metallic bismuth. The target metal cations were simultaneously reduced to the respective metals and were preconcentrated on the electrode surface by forming an alloy with bismuth. Then, an anodic voltammetric scan was applied in which the metals were oxidized and stripped back into the solution; the voltammogram was recorded and the stripping peak heights were related to the concentration of Cd(II) and Pb(II) ions in the sample. Various key parameters were investigated in detail and optimized. The effect of potential interferences was also examined. Under optimum conditions and for preconcentration period of 4 min, the 3σ limit of detection was 1.3 μg L⁻¹ for Pb(II) and 0.37 μg L⁻¹ for Cd(II), while the reproducibility of the method was 4.2% for lead (n = 5, 10.36 μg L⁻¹ Pb(II)) and 3.9% for cadmium (n = 5, 5.62 μg L⁻¹ Cd(II)). Finally, the sensors were applied to the determination of Cd(II) and Pb(II) ions in water samples.     

Separations involving sulphides : Separation of (a) bismuth,lead and cadmium from mercury,and (b) bismuth and mercury from indium

It has been shown that 2N sodium sulphide reagent can be successfully used in the seperation and estimation of: (a) bismuth, lead and cadmium from mercury, and (b) bismuth and mercury from indium     

Cadmium(II) binding by soil-derived fulvic acid measured by anodic stripping voltammetry

Titrations of aqueous solutions of soil fulvic acid (30, 45, and 60 mg l^-1) with cadmium ion solutions at pH 6 and 7 reveal unusual shapes in the stripping current (i_s) vs. total cadmium ion (C_cd²⁺) curves. The expected inflections occur in the titration curves at 8–16 μM. at pH 6 and 12–26 μM at pH 7. In addition, there is an initial rapid increase in i_s at very low C_cd²⁺. The initial rapid increase in current is attributed to labile cadmium—fulvic acid complexes that contribute to i_s by rapid dissociation. Subsequent addition of cadmium ion results in moderately labile complexes and i_s becomes partially kinetically controlled. The stripping current was corrected for kinetic current contributions from dissociation of complexes, and total ligand concentrations, conditional stability constants, and upper slopes were calculated from data well past the titration end-point. The use of upper slopes after kinetic current corrections as in situ calibration curves, allowed calculations of equilibrium cadmium concentrations. The data show that both kinetic current corrections and in situ calibration curves are necessary to avoid substantial errors in calculations of equilibrium cadmium concentrations from anodic stripping voltammetric experiments.     

Voltammetric Determination of Mercury(II) at Poly(3‐hexylthiophene) Film Electrode. Effect of Halide Ions

The well‐known method for the determination of mercury(II), which is based on the anodic stripping voltammetry of mercury(II), has been adapted for applications at the thin film poly(3‐hexylthiophene) polymer electrode. Halide ions have been found to increase the sensitivity of the mercury response and shift it more positive potentials. This behavior is explained by formation of mercuric halide which can be easily deposited and stripped from the polymer electrode surface. The procedure was optimized for mercury determination. For 120 s accumulation time, detection limit of 5 ng mL^?1 mercury(II) has been observed. The relative standard deviation is 1.3% at 40 ng mL^?1 mercury(II). The performance of the polymer film studied in this work was evaluated in the presence of surfactants and some potential interfering metal ions such as cadmium, lead, copper and nickel.     

The molten phase conductance and the thermotropic phase transition in lead(II), zinc(II) and cadmium(II) 10-hydroxyoctadecanoates

The electrical conductances and heats of phase changes in lead(II), zinc(II) and cadmium(II) 10-hydroxyoctadecanoates are measured. The soaps are prepared by metathesis in alcohol solution from 10-hydroxyoctadecanoic acid which in turn is prepared from the oxidation of cis-9-octadecenoic (oleic) acid with concentrated sulphuric acid.The Arrhenius plot for lead(II) 10-hydroxyoctadecanoate shows a maximum, a behaviour that had earlier been interpreted to be due to complex formation. A similar plot for zinc(II) 10-hydroxyoctadecanoate is linear while that for cadmium(II) 10-hydroxyoctadecanoate presents a discontinuity which is interpreted, with the aid of the differential scanning calorimetric (DSC) spectra and optical examination, to be suggestive of the formation of an intermediate phase between the solid and the liquid phases. The low conductances of the soaps in comparison with the literature data on some metal caboxylates indicate the existence of extensive intermolecular hydrogen bonding in the molten phase. Both lead(II) and zinc(II) 10-hydroxyoctadecanoates melt directly from the solid to the liquid phase while their cadmium(II) counterpart passes through the gel-like phase before melting into the liquid. The mesophase of cadmium(II) 10-hydroxyoctadecanoate is transformed to the liquid phase with a relatively low enthalpy change and the behaviour is associated with the cylindrical micekkar structures of the liquid phase that have their formative stage from the gel-like mesophase.     

Electroanalytical Determination of Cd(II) and Pb(II) in Bivalve Mollusks using Electrochemically Reduced Graphene Oxide‐based Electrode

An electrochemical sensor for the simultaneous determination of Cd(II) and Pb(II) by square wave anodic stripping voltammetry (SWASV) in bivalve mollusks using a glassy carbon electrode modified with electrochemically reduced graphene oxide has been developed. The modified surface was characterized by cyclic voltammetry, high resolution scanning electron microscopy (HR‐SEM), and Raman spectroscopy. The optimum conditions were optimized and a linear range was observed from 15–105 μg L^?1 with a limits of detection of 15 μg L^?1 for Cd(II) and Pb(II). The methodology was validated and applied in different samples of commercial bivalve mollusks with satisfactory results. The high conductivity and greater surface area of the modifying agent improves the preconcentration capacity of the electrochemical sensor, allowing to develop a simple, rapid and sensitive analysis in the detection of lead and cadmium in marine resources.